To determine the order of nucleophilicity for the species \( CH_3^- \), \( NH_2^- \), \( OH^- \), and \( F^- \), we need to analyze the stability of the negative charges on each of these species and their ability to donate electrons.
### Step 1: Understand Nucleophilicity
Nucleophilicity refers to the ability of a species to donate a pair of electrons. A stronger nucleophile is one that can more readily donate its electrons.
**Hint:** Consider the factors that influence nucleophilicity, such as charge, electronegativity, and the stability of the negative charge.
### Step 2: Analyze Each Species
1. **\( CH_3^- \)**: The negative charge is on carbon, which is less electronegative than nitrogen, oxygen, and fluorine. This makes \( CH_3^- \) a strong nucleophile because carbon can easily donate its electron pair.
2. **\( NH_2^- \)**: The negative charge is on nitrogen, which is more electronegative than carbon but less than oxygen and fluorine. Nitrogen can also donate its electron pair effectively, making it a good nucleophile, but not as strong as \( CH_3^- \).
3. **\( OH^- \)**: The negative charge is on oxygen, which is more electronegative than both carbon and nitrogen. Although \( OH^- \) can donate electrons, its higher electronegativity means it holds onto its electrons more tightly compared to \( CH_3^- \) and \( NH_2^- \).
4. **\( F^- \)**: The negative charge is on fluorine, which is the most electronegative element. This means \( F^- \) holds onto its electrons very tightly, making it the weakest nucleophile among the four.
**Hint:** Compare the electronegativities of the atoms involved to understand how they affect the stability of the negative charge.
### Step 3: Determine the Order of Nucleophilicity
Based on the analysis:
- \( CH_3^- \) is the strongest nucleophile because it has the least electronegative atom holding the negative charge.
- \( NH_2^- \) follows as it is less stable than \( OH^- \) but more stable than \( CH_3^- \).
- \( OH^- \) is next due to the higher electronegativity of oxygen.
- \( F^- \) is the weakest nucleophile because fluorine holds onto its electrons the most tightly.
Thus, the order of nucleophilicity is:
\[ CH_3^- > NH_2^- > OH^- > F^- \]
### Final Answer
The nucleophilicities of \( CH_3^- \), \( NH_2^- \), \( OH^- \), and \( F^- \) decrease in the order:
\[ CH_3^- > NH_2^- > OH^- > F^- \]
